Composition and method for controlling phosphonates tending to precipitate metal ions in water

ABSTRACT

A method for controlling phosphonates which tend to precipitate with metal ions in water treatment operations comprising, adding to the water a water-soluble copolymer containing one or more of the following monomeric units:    &lt;IMAGE&gt;  [a]  in which: R is hydrogen or an alkyl group, R1 is an alkyl group and X is hydrogen, NH4+, a water soluble metal ion or organic base; and [b] a monocarboxylic acid monomer; and adding the copolymer to the water to be treated in an amount sufficient to prevent precipitation of said phosphonates.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/301,161, filed Sep. 6,1994 U.S. Pat. No. 5,453,416; which is a Continuation of U.S. Ser. No,07/868,079, filed Apr. 13, 1992; which is a Continuation-in-Part of U.S.Ser. No. 07/701,301, filed May 13, 1991; which is a Continuation of U.S.Ser. No. 07/372,121, filed Jun. 27, 1989; which is aContinuation-in-Part of U.S. Ser. No. 07/078,799, filed Jul. 28, 1987which all abandoned.

FIELD OF THE INVENTION

This invention relates to a composition and method for controllingphosphonates which normally tend to precipitate with metal ions such ascalcium and zinc in water treatment systems.

BACKGROUND OF THE INVENTION

Natural water typically contains many salts which form ions in solution.All these ions are involved in chemical equilibria. The solubility ofthe different chemical species is described by the solubility product.If the solubility product of a chemical species is exceeded, solidproducts can precipitate out of solution and produce deposits onsurfaces in contact with the aqueous solution. These deposits can giverise to severe problems in industrial aqueous equipment such as heatexchangers in cooling systems, boilers, evaporators, etc. The mostcommon deposits which form on aqueous equipment surfaces are calciumcarbonate, calcium sulfate, calcium phosphate, zinc hydroxide, zincphosphate, silicates and iron oxides.

To overcome these problems, deposit control chemicals such asphosphonates and polymers have been used to treat these systems. At verylow (substoichiometric) treatment levels, these deposit controlchemicals inhibit the nucleation and growth of crystals.

For example, U.S. Pat. Nos. 3,904,522 and 3,928,196 describe the use ofpolyacrylic acid and hydrolyzed polyacrylamide as scale inhibitors forCaCO₃ and CaSO₄. U.S. Pat. No. 3,928,196 describes the use of acrylicacid-2-acrylamido-2-methylpropylsulfonic acid (AMPS) copolymer as anantiprecipitant for calcium carbonate and calcium sulfate. U.S. Pat. No.3,806,367 teaches the use of acrylic acid-AMPS copolymers in preventingand removing iron oxide deposits.

Prior to about 1980, there were no commercially available polymers orphosphonates which could prevent calcium phosphate, zinc hydroxide andzinc phosphate deposit formation. The copolymer acrylicacid-hydroxy-propylacrylate was first described as preventing thesedeposits (European Patent Application 0 017 373). Since 1980 many otherpolymers have been developed which are also able to prevent zinchydroxide, zinc phosphate and calcium phosphate deposits. For example,European Patent Application 0 142 929 and U.S. Pat. No. 4,288,327describe the use of acrylic acid-sulfonate ether copolymers as phosphateantiprecipitants.

The most widespread phosphonates are hydroxyethylidene phosphonic acidand nitrilotrimethylenephosphonic acid. Phosphonates are also used ascorrosion inhibitors. However, the use of phosphonates as scale andcorrosion inhibitors in water treatment has left some importantproblems. As is known from the literature, many of the commonly usedphosphonates form insoluble phosphonate salts with cations, such as, forexample, calcium and zinc.

Until now only sulfonate containing polymers were known to preventcalcium and zinc phosphonate deposits. For example, European PatentApplication 0 142 929 and European Patent Application 0 122 013 describethe use of sulfonate containing polymers for this purpose.

Now, surprisingly, it has been found that sulfate containing polymersalso exhibit zinc and calcium phosphonate stabilizing properties.Sulfate containing polymers have been known for a number of years. Forexample, U.S. Pat. No. 3,839,393 describes the synthesis andpolymerization of sulfatoalkane acrylates and methacrylates. U.S. Pat.No. 4,036,788 describes anionic hydrogels based on sulfate containingmonomers. However, in the literature phosphonate stabilizing propertiesof sulfate containing polymers have never been described, suggested orrecognized. While U.S. Pat. No. 4,036,788 to Steckler is involved withthe complexation of basic cationic materials onto anionic hydrogelswhich are stable, three dimensional, water-insoluble copolymer networks,the present invention is directed to water treatment withsubstoechiometric amounts of the water-soluble polymers disclosed.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates the enhanced solubility of phosphonates (PO₄ ³⁻) inan aqueous solution treated with the polymer of the invention relativeto an aqueous solution treated with a polyacrylic acid polymer.

SUMMARY OF THE INVENTION

One object of the invention is to provide a new and original method forcontrolling such phosphonates in water treatment.

In accordance with the present invention, there has been provided amethod for treating an aqueous system containing metal ions to inhibitor prevent the precipitation of phosphonates with the metal ions whichcomprises adding to the system a water-soluble copolymer containing atleast the following monomeric units: ##STR2## where R is hydrogen oralkyl; R₁ is an alkyl group and X is hydrogen, NH⁺ ₄, a water solublemetal ion or an organic base; and

[b] a monocarboxylic acid monomer.

The preferred monocarboxylic acid is acrylic acid or methacrylic acid.

Other features and advantages of the invention will appear from thedetailed description set forth hereinafter.

It has been discovered that when adding to a water solution a newpolymer according to the invention in combination with phosphonateswhich normally tend to precipitate out in high calcium containing water,essentially no precipitation of insoluble phosphonate compounds willoccur. In addition the protection against corrosion will be remarkableimproved.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to a method for treating an aqueoussystem containing metal ions to inhibit or prevent the precipitation ofphosphonates with the metal ions which comprises adding to the system awater-soluble polymer containing at least the following monomers;##STR3## where R is hydrogen or alkyl; R₁ is an alkyl group and X ishydrogen NH⁺ ₄, a water soluble metal ion or an organic base. An exampleof this type of monomer is the sulfuric ester of2-hydroxyethylmethacrylate (HEMA);

[b] Monocarboxylic acid monomers, such as acrylic acid or methacrylicacid. These acids may be neutralized to the salt form with bases suchas, for example, sodium hydroxide, ammonia, and organic bases as, forexample, ethanolamine.

Also part of these carboxylic acids may be replaced by other monomerunits, such as:

dicarboxylic acids such as maleic acid or anhydride, itaconic acid andthe like;

sulfonate containing monomers such as2-acrylamido-2-methylpropylsulfonic acid, methallylsulfonic acid,vinylsulfonic acid and the like;

hydroxy-containing monomers such as 2-hydroxypropylacrylateallyl-alcohol and the like;

esters of the aforementioned monomers, for example, ethylacrylate,methylmethacrylate, the phosphate ester of hydroxyethylmethacrylate;

phosphorus bearing monomers like vinylphosphonic acid,allylhydroxypropylphosphonate, etc.; and

other copolymerizable units which include acrylamide, acrylonitrile,vinylacetate, acroleine, or cationic monomers, and mixtures thereof.

The polymers may be produced, for example, by simple polymerizationtechniques involving free radicals with water as a solvent, as are wellknown to those of skill in this art. Common chemicals such aspersulfate, hydrogen peroxide and benzoylperoxide may be used asinitiators. To regulate the chain length, well known materials such assulfur bearing compounds, e.g. mercaptoacetic acid, mercaptoethanol andso forth may be used. Other chain transfer agents are, for example,phosphorus bearing compounds such as H₂ PO₃, H₃ PO₂ and organicphosphorus bearing compounds such as, for example, dialkylphosphite.Also, alcohols, for instance, isopropanol may be used.

The molecular weight of the polymer may vary between about 500 to about100,000, with about 1000 to 10,000 being preferred. The ratio of [a] to[b] monomers, as referred to above, may vary from 30:1 to 1:30. Therange of preferred ratios is 1:30 to 1:2.

The above described polymers are added to the aqueous system in amountsthat are substoichiometric with respect to the metal ions which arepresent in the system and generally demonstrate their phosphonatestabilizing properties in the dose range of about 0.1 to 100 ppm; 1 to20 ppm being preferred.

To control phosphonate deposits the aforementioned polymers may becombined with other polymers. Examples of such polymers are:

polymonocarboxylic acid, e.g. polyacrylic acid, phosphinocarboxylicacids;

polydicarboxylic acids, e.g. polymaleic acid;

polyacrylamide

copolymers of monocarboxylic or dicarboxylic acids with othercopolymerizable units, such as:

sulfonate containing monomers, as for example,2-acrylamido-2-methyl-propylsulfonic acid, methallylsulfonic acid,styrene sulfonic acid;

hydroxy-containing monomers, such as 2-hydroxy-propyl-acrylate,allyl-alcohol;

esters of the aforementioned carboxylic acids, such as ethylacrylate,methylmethacrylate etc.

aldehyde containing monomers, e.g. acroleine;

amides, e.g. acrylamide; and

phosphorus bearing monomers, such as vinylphosphonate,allylhydroxypropylphosphonate, hydroxyethylmethacrylate phosphate.

Also included within the intended copolymers are the copolymers bearingphosphine groups as mentioned in European Patent Application 0 150 706,and polysulfonic acids, such as polystyrenesulfonate.

This above listing of admixed polymers merely serves as an illustrationand is not intended to be a limitation on the scope of the presentinvention.

In addition to the above set forth compositions and solutions, use canbe made of other water treating chemicals such as:

zinc, inorganic phosphorus compounds such as orthophosphatepolyphosphates, organic phosphates which stay in solution at highcalcium levels;

iron complexing agents such as citric acid, gluconic acid;

passive film forming agents such as mono or polycarboxylic longaliphatic chain or cycloaliphatic di- and polycarboxylic acids;

copper protecting chemicals such as benzotriazole,mercaptobenzothiazole, tolyltriazole; and

silicates.

Water to be treated according to the invention may include coolingwater, boiler water, water in water scrubber units, and so on.

EXAMPLES

The following examples illustrate the merits of the invention. In theseexamples use is made of the code set forth below:

    ______________________________________                                        Polymer                      Code                                             ______________________________________                                        Polyacrylic Acid             1                                                Copolymer sulfuric ester of hydroxyethylene-                                                               2                                                methacrylic acid (HEMA-S)35%-Acrylic acid                                     (AA)65%                                                                       Terpolymer HEMA-S(30%)-AA(60%)-maleic acid                                                                 3                                                Terpolymer HEMA-S(30%)-AA(60%)-Hydroxypropyl-                                                              4                                                acrylate(10%)                                                                 Terpolymer HEMA-S(20%)-AMPS(15%)-AA(65%)                                                                   5                                                HEMA-S(35%)-AA(60%)-allylalcohol(10%)                                                                      6                                                HEMA-S(30%)-AA(60%)-acrylamide(10%)                                                                        7                                                HEMA-S(30%)-AA(60%)-allyhydroxypropyl-                                                                     8                                                phosphonate(10%)                                                              ______________________________________                                    

Example 1

A 10 ppm solution of different well known phosphonates was brought intocontact with a 1000 ppm solution of Calcium at a temperature of about60° C. for about 30 minutes, at pH 9, and then mixed together with apolymer. After a period the turbidity of the sample was measured at 450nm. The sample was then filtered over a millipore filter of 0.22 um andthe soluble phosphonate was determined. The results are shown below inTable 1.

                                      TABLE 1                                     __________________________________________________________________________    Stabilization of Different Phosphates at pH 9;                                Turbidity of Calcium Measured; 1000 ppm CaCO.sub.3                                                            Soluble Phosphonate                           Phosphonate    Additive                                                                             Turbidity at 450 nm                                                                     (ppm as PO.sub.4.sup.3-)                      __________________________________________________________________________    10 ppm nitrilotrimethylene                                                                   none   0.019     3.82                                          phosphonic acid (NTMPA)                                                       10 ppm nitrilotrimethylene                                                                   10 ppm 1                                                                             0.017     4                                             phosphonic acid (NTMPA)                                                       10 ppm hydroxyethylidene-                                                                    none   0.020     3.6                                           diphosphonic acid (HEDP)                                                      10 ppm hydroxyethylidene-                                                                    10 ppm 0.002     8.2                                           diphosphonic acid (HEDP)                                                                     copolymer 2                                                    10 ppm hydroxyethylidene-                                                                    10 ppm 1                                                                             0.018     3.9                                           diphosphonic acid (HEDP)                                                      5 ppm HEDP-5 ppm NTMPA                                                                       none   0.019     4.01                                          5 ppm HEDP-5 ppm NTMPA                                                                       10 ppm 0.002     9.04                                                         copolymer 2                                                    5 ppm HEDP-5 ppm NTMPA                                                                       10 ppm 0.017     4.4                                                          copolymer 2                                                    10 ppm NTMPA   10 ppm 0.005     7.2                                                          terpolymer 3                                                   10 ppm HEDP    10 ppm 0.006     6.9                                                          terpolymer 3                                                   10 ppm NTMPA   10 ppm 0.006     7.1                                                          terpolymer 4                                                   10 ppm HEDP    10 ppm 0.006     6.8                                                          terpolymer 4                                                   10 ppm NTMPA   10 ppm 0.004     7.9                                                          terpolymer 5                                                   10 ppm HEDP    10 ppm 0.003     8.0                                                          terpolymer 5                                                   10 ppm NTMPA   10 ppm 0.005     7.3                                                          terpolymer 6                                                   10 ppm HEDP    10 ppm 0.005     7.4                                                          terpolymer 6                                                   10 ppm NTMPA   10 ppm 0.005     7.2                                                          terpolymer 7                                                   10 ppm HEDP    10 ppm 0.005     7.3                                                          terpolymer 7                                                   10 ppm NTMPA   10 ppm 0.005     7.4                                           10 ppm NTMPA   10 ppm 0.005     7.4                                                          terpolymer 8                                                   10 ppm HEDP    10 ppm 0.006     7.0                                                          terpolymer 8                                                   __________________________________________________________________________

Example 2

The same effects are observed when adding at pH 9 a supplement of zincions to the solution. This is demonstrated in the next table, where asupplement of 2 ppm zinc is added to the solution.

                                      TABLE 2                                     __________________________________________________________________________    Stabilization of Various Solutions 1 with Addition of 2 ppm Zinc                                         Soluble phosphonate                                                                     Soluble Zinc                             Phosphonate    Additive                                                                             Turbidity                                                                          (ppm as PO.sub.4.sup.3-)                                                                (ppm Zn)                                 __________________________________________________________________________    10 ppm NTMPA   none   0.005                                                                              8.72      0.58                                     10 ppm HEDP    none   0.020                                                                              2.20      0.34                                     5 ppm HEDP-5 ppm NTMPA                                                                       none   0.020                                                                              5.88      0.78                                     10 ppm NTMPA   5 ppm  0.002                                                                              9.6       0.75                                                    copolymer 2                                                    10 ppm HEDP    5 ppm  0.010                                                                              3.22      0.69                                                    copolymer 2                                                    5 ppm HEDP-5 ppm NTMPA                                                                       5 ppm  0.003                                                                              8.5       1.16                                                    copolymer 2                                                    10 ppm NTMPA   10 ppm 0.002                                                                              8.80      0.56                                                    copolymer 2                                                    10 ppm HEDP    10 ppm 0.002                                                                              7.76      1.60                                                    copolymer 2                                                    5 ppm HEDP-5 ppm NTMPA                                                                       10 ppm 0.002                                                                              8.17      1.38                                                    Sopolymer 2                                                    10 ppm NTMPA   10 ppm 0.0005                                                                             7.4       1.20                                                    terpolymer 3                                                   10 ppm HEDP    10 ppm 0.006                                                                              7.1       1.10                                                    terpolymer 3                                                   10 ppm HEDP    10 ppm 0.006                                                                              6.9       1.05                                                    terpolymer 5                                                   10 ppm NTMPA   10 ppm 0.002                                                                              8.5       1.42                                                    terpolymer 5                                                   10 ppm HEDP    10 ppm 0.003                                                                              8.4       1.39                                                    terpolymer 6                                                   10 ppm NTMPA   10 ppm 0.005                                                                              7.4       1.03                                                    terpolymer 6                                                   10 ppm HEDP    10 ppm 0.006                                                                              7.3       1.10                                                    terpolymer 7                                                   10 ppm NTMPA   10 ppm 0.005                                                                              7.5       1.20                                                    terpolymer 7                                                   10 ppm HEDP    10 ppm 0.006                                                                              7.1       1.13                                                    terpolymer 8                                                   10 ppm NTMPA   10 ppm 0.005                                                                              7.5       1.23                                                    terpolymer 8                                                   10 ppm HEDP    10 ppm 0.005                                                                              7.6       1.28                                                    terpolymer 8                                                   __________________________________________________________________________

Example 3

The HEMA-S-acrylic acid copolymer was also tested in a pilot coolingsystem under an all organic program containing 3 ppm NTMPA, 2 ppm HEDP,2 ppm phosphono-butane-1,2,4-tricarboxylic acid (PBTC). The waterquality of the cooling water is indicated below:

    ______________________________________                                        pH:                  8.6                                                      TAC (ppm CaCO.sub.3):                                                                              500                                                      TA (ppm CaCO.sub.3): 30                                                       Cl:                  260 ppm                                                  SO.sub.4.sup.2- :    240 ppm                                                  TDS:                 1500 μS cm.sup.-1                                     TCa (ppm CaCO.sub.3):                                                                              500                                                      ______________________________________                                    

The water temperature of the cooling water was about 50° C.; theretention time of the cooling system was 3 days.

When using 5 ppm HEMA-S-acrylic acid copolymer as a polymer constituent,no phosphonate loss was observed during 7 days, while corrosion wascompletely under control.

Substituting the HEMA-S-acrylic acid copolymer for simple polyacrylicacid, the soluble phosphonate content dropped fast, heavy calciumphosphonate deposits resulted and under the deposit corrosion tookplace. The difference in phosphonate solubility between the twotreatments is given in the Figure.

I claim:
 1. A composition of matter, comprising; a water solublecopolymer having a molecular weight from about 500 to about 100,000containing the following monomeric units (a) and b): ##STR4## in which:R is hydrogen, or an alkyl group,R₁ is an alkylene group and X ishydrogen, NH⁺ ₄, a water soluble metal ion or an organic base; and (b) amonocarboxylic acid monomer selected from the group consisting ofacrylic acid and methacrylic acid.
 2. The composition of claim 1,wherein the monomer unit is the sulfuric ester of2-hydroxyethylmethacrylate.
 3. The composition of claim 1, wherein thecarboxylic acid is neutralized by an inorganic or organic base.
 4. Thecomposition of claim 1, wherein the monomeric unit referred to in is amixture of sulfate containing monomers.
 5. The composition of claim 1,wherein the molar ratio between the monomers referred to in and variesbetween 30:1 to 1:30.
 6. The composition of claim 5, wherein the molarratio varies between 30:0 and 1:2.
 7. The composition of claim 1,wherein said copolymer is in an aqueous solution in a concentration ofabout 0.1 ppm to 100 ppm.
 8. The composition of claim 7, wherein saidcopolymer is in a concentration of about 1 to about 20 ppm.
 9. Acomposition of matter, comprising:an aqueous phosphonate containingsolution of a copolymer having a molecular weight from about 500 toabout 100,000 wherein the concentration of the copolymer in the solutionis within the range 0.1 to 100 ppm and wherein the copolymer containsthe following monomeric units (a) and (b): ##STR5## in which: R ishydrogen, or an alkyl group, R₁ is an alkylene group and X is hydrogen,NH⁺ ₄, a water soluble metal ion or an organic base; and (b) amonocarboxylic acid monomer selected from the group consisting ofacrylic acid and methacrylic acid.
 10. A composition of claim 9 whereinthe concentration of the copolymer is within the range 1 to 20 ppm.